Oxidation and interdiffusion behavior of a germanium-modified silicide coating on an Nb–Si-based alloy

To investigate the interdiffusion behavior of Ge-modified silicide coatings on an Nb–Si-based alloy substrate, the coating was oxidized at 1250°C for 5, 10, 20, 50, or 100 h. The interfacial diffusion between the (Nb,X)(Si,Ge) 2 (X = Ti, Cr, Hf) coating and the Nb–Si based alloy was also examined. The transitional layer is composed of (Ti,Nb) 5 (Si,Ge) 4 and a small amount of (Nb,X) 5 (Si,Ge) 3 . With increasing oxidation time, the thickness of the transitional layer increases because of the diffusion of Si from the outer layer to the substrate, which obeys a parabolic rate law. The parabolic growth rate constant of the transitional layer under oxidation conditions is 2.018 μm·h −1/2 . Moreover, the interdiffusion coefficients of Si in the transitional layer were determined from the interdiffusion fluxes calculated directly from experimental concentration profiles.